The standard definition of a transient ischemic attack--"a cerebral dysfunction of an ischemic nature lasting no longer than 24 hours with a tendency to recur"--was arrived at arbitrarily and is no longer tenable. Experience shows that attacks are much briefer, usually less than an hour, and many are associated with brain infarction. A newer definition, more consonant with the data, is preferred--"transient ischemic attack is a brief episode of neurological dysfunction caused by focal brain or retinal ischemia, with clinical symptoms typically lasting less than an hour, and without evidence of acute infarction." Patients with transient ischemic attacks require urgent evaluation that includes brain and vascular imaging, blood tests, and often cardiac investigations. Treatment will depend on the nature of the causative cervico-cranial vascular, cardiac, and hematologic abnormalities found on investigation.